Wordpad, the program that comes with current versions of Windows, saves in Word 6 format.

What's up, DOC?

But just because the file you stumbled onto has a DOC extension doesn't mean it is necessarily actually an MS Word file, though if it's not that old it probably is. Older files, like from the 1980s or 1990s, might be something else entirely. Several other word processors in that era used .DOC file extensions, even though their format was nothing like MS Word's. Also, it was fairly common for people to save plain text files with that extension when they were DOCumenting something, like the instructions for a program that was packed up in an ARC or ZIP file for download on a bulletin board system (BBS). But you might still try opening them with Word (as will normally happen in Windows if you have Word installed and double-click on a DOC file), since it will open plain-text files all right (even ancient ones).

Copy all the resulting *.cnv files (but most importantly Doswrd32.cnv) to C:\Program Files (x86)\Common Files\microsoft shared\TextConv (For users with a 32-bit Windows it is just C:\Program Files\Common Files\microsoft shared\TextConv)

(Re)Start Microsoft Word

Open the old Word file via the Open-dialog within Word.

Word will show a prompt informing you that a text converter has to be started and that this might impose a security risk which you should only do if you trust the source where you got the files from. Press OK (if you trust the source of the files).

Word will most likely show a prompt like "Style Sheet D:/STANDARD.DFV not found". Press Ok. Now a file selector dialog will open asking you to select a style sheet (*.sty) file. If you do have a style sheet for the file then select this. Otherwise create a new empty file in the regular Windows Explorer, rename it "empty.sty" and select it in the file selector. Selecting such an empty file could cause opened file to lose some general properties like print margins etc.

Now you should be able to see the Word for DOS file within the modern Microsoft Word.

Opening earlier Word for Windows files in a modern Microsoft Word

While various Word for Windows formats are still supported (unlike the DOS ones noted above), some of them are now disabled by default for security reasons, as Microsoft thinks that their own legacy code to open them is vulnerable to risks. Thus, in order to open such files, you may need to make registry changes, documented in a help page linked below.